1. Field of the Invention
The present invention relates to a position detecting apparatus and a position detecting method that are suitable for detecting an edge position of a substrate.
2. Description of the Related Art
Recently, Extreme Ultraviolet (EUV) lithography, which is a projection exposure technique of a reduced-reflection type that uses a soft X-ray of 5 nanometers to 15 nanometers, is considered to be one of the most promising candidates for the next-generation lithography technique. The development of EUV lithography is pursued on a world-wide scale.
One of the issues that need attention while implementing the EUV lithography technique is how to deal with foreign substances on masks. Particles adhering to EUV masks in the manufacturing process thereof greatly influence the yield of the EUV masks, just like in the example of ordinary photomasks that are currently in the market. For the ordinary photomasks, protection covers called pellicles are used to prevent particles from adhering to the photomasks. However, it is not possible to use pellicles in an EUV ray region. Thus, preventing particles from adhering to EUV masks in the manufacturing process thereof is a major issue.
Also, adhesions of particles can cause a problem whenever EUV masks on which a pattern is formed are used in the manufacturing process of semiconductors. For example, when an EUV mask is carried into (or carried out from) a case or a pod, if the EUV mask touches the case or the pod, particles that are caused by the touching may adhere to the EUV mask. As another example, when an EUV mask is carried into (or carried out from) a vacuum apparatus such as a dry etching apparatus, during a vacuuming (pumping down) process (or an air-venting process) performed in a load-lock chamber, particles that are present in the load-lock chamber or particles that are brought into the load-lock chamber when the EUV mask is carried therein may be stirred up because of the vacuuming (pumping down) process (or the air-venting process) and may adhere to the EUV mask. The same problem can also occur in an EUV exposure apparatus, which is a type of vacuum apparatus.
To prevent particle adhesions, for example, it has been suggested that a cover-like structure designed to block such particles should be mounted over an EUV mask so that the surface of the EUV mask is protected. The cover-like structure is configured so that it can be attached to and detached from the EUV mask and is called a removable pellicle. Different types of structures such as ones in the form of a tray and a bracket have been proposed as configuration of removable pellicles. In any case, these removable pellicles are used for the purpose of preventing particles from adhering to the pattern-forming surface side of EUV masks, either by mounting a removable pellicle over an EUV mask or mounting an EUV mask over a removable pellicle. As disclosed in JP-A 2002-299225 (KOKAI), JP-A 2006-184442 (KOKAI), and JP-A 2005-268464 (KOKAI), mechanical supporting pins or pads made of a resin is used in parts of each removable pellicle that are in contact with an EUV mask. Each removable pellicle holds the upper and the lower faces or the lateral faces of an EUV mask via those parts that are in contact with the EUV mask.
Accordingly, like in the example above in which the EUV mask is carried into (or carried out from) a case or a pod, when an EUV mask is attached to or detached from a removable pellicle, particles occur when the EUV mask comes into contact with (or comes out of contact with) the removable pellicle. In addition, when an EUV mask is transported while being attached to a removable pellicle, particles occur if the EUV mask and the removable pellicle rub against each other. In such a situation, if the positional relationship between the EUV mask and the removable pellicle is not a proper one, the size of the areas of the parts of the supporting pins or the pads of the removable pellicle that are in contact with the EUV mask becomes larger. As a result, a larger amount of particles will occur. To avoid this situation, before an EUV mask is attached to a removable pellicle, it is necessary to detect the positions of the EUV mask and the removable pellicle, so that if the positional relationship between them largely differs from a proper one, the attaching process should be stopped for a while, and the positional relationship can be corrected.
JP-A 2004-214658 (KOKAI) discloses a method for detecting the position of a mask by detecting a mark formed on the mask through a transparent window provided in a container. Also, JP-A 2006-153899 (KOKAI) discloses a method for detecting the positions of a mask and a mask protecting member by detecting position measuring marks that are formed on the mask and the mask protecting member, respectively. Both of these methods are characterized in that the position of the mask (or the mask protecting member) is detected by detecting the mark that is formed, in advance, in the mask (or in the mask protecting member).
Particles can adhere not only to a mask on which a pattern (or a mark used for measuring the position) has already been formed, but also to a mask blank on which a pattern has not yet been formed. Thus, it is necessary to realize a position detecting method that can be used with mask blanks. For this purpose, it is necessary to detect the position of each mask blank with a high level of precision, without being influenced by the material of which the mask blank is made, the material of which a film is formed, and the state in which the film is formed. To achieve this goal, the inventors of the present application have proposed a method in which, while light is radiated on a mask or a mask blank from the direction of a lateral face thereof, an image of a portion that includes a substrate edge of the mask or the mask blank is taken from the front surface (or the rear surface) thereof so that the position of the substrate edge is measured based on the image of scattered light on the substrate edge that has been taken (Japanese Patent No. 3795820).
According to this method, however, the level of precision in the position detection process can be low, depending on the shape of the substrate edge of the mask or the mask blank. In some situations, it is not possible to accurately detect the position of the substrate.
In addition, in some situations, depending on the shape of the substrate edge of the mask or the mask blank, it is not possible to accurately detect the position of the substrate while the substrate is attached to a cover-like structure such as a removable pellicle.